1. Field of the Invention
This invention relates generally to a control mechanism wherein axial and rotary movements are transmitted between articulated frames by means of a shaft system which articulates about an axis not coincident with the pivot axis of the frames. More particularly, the invention relates to a shift control mechanism for a gear transmission wherein the shaft system has a collapsible section with a cable spanning the section, so as to effect transmission of rotary and axial movements between a gear shift actuator on the main frame and a shift control on the subframe.
2. Description of the Prior Art
In a remotely controlled mechanism such as a gear transmission for a motor vehicle, both axial and rotary shifting movements of the gear actuator are transmitted to the shift control of the gear transmission by means of a shift system. Transmission of such motion normally does not present a problem for present motor vehicles including tractor-trailer vehicles which utilize a cab-forward or a high-tilt conventional cab configuration. With such an arrangement, the cab, the cab-mounted shift controls, the transmission and the transmission-mounted shift controls are all attached to the main chassis frame. Some relative articulations occur due to the elastomeric mounting of both the cab and the transmission, although such articulation is relatively insignificant.
The problem in both effectively transmitting axial and rotary movements from the cab-mounted gear actuator to the gear transmission shift control is when the latter is mounted on a sub-frame for pivotal movement relative to the cab-mounted main frame. The shaft system in such an arrangement is therefore fixed at the cab end and articulates at its opposite ends about an axis other than the pivotal axis between the main frame and the sub-frame. Accordingly, any up-and-down movements of the sub-frame relative to the main frame causes changes in the effective length of the shaft between the gear transmission control and the gear actuator.
A solution employed for reducing or eliminating the problem, particularly on tilt-cab trucks, is to so arrange the centerline of the shift lever sphere as to coincide with the tilt axis of the cab. However, such an arrangement requires an extremely complex mechanical linkage which is quite often only reasonably effective.